Field of the invention

The present invention relates to a cutting machine and parts thereof, the cutting machine comprising two cutter assemblies arranged to rotate in opposite directions around parallel rotational axes. Background of the invention

Within various fields of work, large amounts of waste fibrous materials, often in the form of cut off pieces from lengths or carpets, are deposited due to lack of machinery for disintegrating the material into single fibres that can be reused for the same as or other purposes than the previous use.

One example of such fibrous materials could be pieces of glass fibre that are left behind when other pieces have been cut out of a length of glass fibre according to patterns designed to fit into a specific mould. For instance, 8-12 % of the glass fibre material is wasted when the fibre -material is cut out in different patterns for producing wind turbine blades.

At present, 1000-1500 tons of waste material is deposited every year from the wind turbine industry in Denmark alone. In 2030, it is expected that 2.2 millions tons of glass fibre will be deposited by the wind turbine industry worldwide. This is in stark contrast to the environmental friendly "green energy" policies otherwise followed by the industry.

Another example could be felt carpets, which can be used only once or at least only a few times for trade fairs and the like and then must be deposited due to the fact that they contain fibres that are extremely flammable. Disintegration of such carpets into a homogeneous material consisting of single fibres of equal lengths would enable for reuse of the material.

Several examples are known of machines for shredding disposable materials into smaller pieces before the materials are placed in different kinds of waste deposits. Many of these machines are of the same type as the solid waste comminutor disclosed in European Patent No. EP 0 629 447 Bl comprising two set of cutters each mounted on a rotational axes, where these axes are parallel and rotate in opposite directions, cutter elements of the one set of cutters interleaving with cutter elements of the other set of cutters.

However, the output from such shredding machines is typically very heterogeneous when it comes to the sizes of the pieces into which a material has been shredded, and even if the shredded material is of a fibrous type, there is not disclosed any means for isolating the single fibres from the shredded pieces of material.

In most cases, the lengths of the isolated fibres must fall within a relatively narrow and well-defined range in order for the fibres to be well-suited for being reused, for instance for producing new fibre glass or for reinforcement of other materials, such as polymer concrete.

It is an object of the present invention to provide a machine and a method for disintegrating fibrous material into single fibres that are suitable for being reused. Brief description of the invention

The present invention relates to a cutting machine for disintegrating fibrous materials, such as un-hardened fabric-type glass fibre, into smaller pieces, said cutting machine comprising two cutter assemblies arranged to rotate in opposite directions around parallel rotational axes and a feeding device, each of the cutter assemblies comprising a series of alternating cutter rings and back pressure rings fixed to each other to rotate with a common rotational speed, each of the cutter rings comprising a number of crushing edges extending in a substantially radial direction from the axis of rotation, the two cutter assemblies being arranged so that the cutter rings of the one cutter assembly interleave with the cutter rings of the other cutter assembly in a relation tight enough to assure a cutting effect perpendicular to the rotational axes between cutter rings interleaving with each other, and so that the crushing edges of the cutter rings of one cutter assembly are in close contact with the back pressure rings of the other cutter assembly, and vice versa, thus creating a crushing effect there between, wherein the back pressure rings are elastic.

Such a machine is advantageous not only in that it enables for processing fibrous materials into a form suitable for being recycling instead of being deposited as is typical the case for this type of materials. Also, making the back pressure rings elastic enables for creating a controlled crushing pressure between the back pressure ring and the crushing edges of the cutter rings of the opposing cutter assembly and reduces the wear on the cutter rings. Furthermore, the elasticity makes the tools self- compensating for wear and deflections.

In an embodiment of the invention, each of the crushing edges is formed by the ridge of a straight longitudinal structure, the cross-section of which is symmetric and basically triangular, and which extends all the way across the surface of the cutter ring in a direction substantially parallel to the centre axis of the cutter ring, the distance between two consecutive crushing edges being uniform all around the cutter ring and larger than the width of each of the longitudinal structures so that a recess is formed between each pair of consecutive crushing edges.

Such a crushing edge shape has proved to be especially advantageous for the disintegration of fibrous materials. In an embodiment of the invention, the feeding device is arranged to feed the material to be cut into smaller pieces into the cutting machine with a conveying velocity corresponding to a common peripheral velocity of the crushing edges of the cutter rings of the two cutter assemblies so as to obtain a disintegration of the material into pieces of controlled homogenous dimensions depending on the width of the cutter rings and the peripheral distance between the edges of two consecutive crushing edges of a cutter ring.

By adjusting the conveying velocity in this way, it is assured that there will be no pulling or crowding of the fibre material to be cut as it enters the cutting part of the machine between the two cutter assemblies.

In an embodiment of the invention, the cutter rings are replaceable enabling the operator of the machine to choose different cutter rings having different dimensions for obtaining different dimensions of the small pieces into which the material is to be disintegrated.

This enables the same cutting machine to be used for producing different sizes of small pieces of fibrous materials.

In an embodiment of the invention, the back pressure rings are replaceable enabling the operator of the machine to choose different back pressure rings defining different crushing pressures depending on the properties of the material to be disintegrated. This enables the same cutting machine to be used for different types of fibrous materials.

In an embodiment of the invention, the cutting machine further comprises a suction device arranged to provide a working area between the two cutter assemblies with suction in order to collect the smaller pieces of material as well as dust and other unwanted by-products from the cutting process. The use of such a suction device is advantageous in at least two ways in that it provides a simple means for collecting the smaller pieces for further treatment and/or packing and at the same time removes dust and lose fibres from the surroundings of the cutting machine.

In a further embodiment of the invention, the suction device is arranged to lead the smaller pieces of material collected from the working area through or passing by a heating device for melting away threads used for stitching fibres of the fibrous material together, thus allowing the smaller pieces to disintegrate into single fibres.

Melting away the threads, which are typically made from polyester, has proved to be an advantageous way of facilitating the disintegration of the small pieces of some kinds of fibrous materials, especially glass fibre, into single fibres.

In a further embodiment of the invention, the single fibres are collected and baled for transportation.

It has proved to be more advantageous to transport the fibres in bales as compared to, for instance, shipping containers or the like.

In an embodiment of the invention, the cutting machine further comprises a scraping device for loosening any fibrous material that might be wedged in between two neighbouring cutter rings of a cutter assembly during the cutting process.

The use of such a scraping device has proved to be a very effective way of avoiding problems with fibrous material getting stuck in the cutter assemblies during operation of the cutting machine. In an aspect of the invention, it relates to a cutter ring comprising a number of crushing edges extending in a substantially radial direction from the axis of rotation of the cutter ring, the cutter ring being designed so that when the cutter ring is placed in one of two cutter assemblies arranged to rotate in opposite directions around parallel rotational axes, each of the cutter assemblies comprising a series of alternating cutter rings and back pressure rings fixed to each other to rotate with a common rotational speed, and the two cutter assemblies being arranged so that the cutter rings of the one cutter assembly interleave with the cutter rings of the other cutter assembly in a tight relation, the crushing edges of the cutter rings of one cutter assembly being in close contact with the back pressure rings of the other cutter assembly, and vice versa, a cutting effect perpendicular to the rotational axes is obtained between the edges of cutter rings interleaving with each other, and a crushing effect parallel to the rotational axes is obtained between the crushing edges of the cutter rings of one cutter assembly and the back pressure rings of the other cutter assembly, wherein each of the crushing edges is formed by the ridge of a straight longitudinal structure, the cross-section of which is symmetric and basically triangular, and which extends all the way across the surface of the cutter ring in a direction substantially parallel to the centre axis of the cutter ring, the distance between two consecutive crushing edges being uniform all around the cutter ring and larger than the width of each of the longitudinal structures so that a recess is formed between each pair of consecutive crushing edges.

Cutter rings with such a crushing edge shape have proved to be especially advantageous for the disintegration of fibrous materials into smaller pieces of well- defined dimensions. Especially, this shape ensures a single, straight cut of the fibres, ensuring that the individual fibres are undamaged, thus keeping their full strength in their full length between the points where they are cut.

In an embodiment of the invention, the number of crushing edges on the cutter ring is between 15 and 40, preferably between 19 and 25. In an embodiment of the invention, the width of the cutter ring in a direction parallel to the rotational axes is between 5 mm and 100 mm, preferably between 20 mm and 50 mm. In an embodiment of the invention, the peripheral distance between two consecutive crushing edges of the cutter ring is between 5 mm and 100 mm, preferably between 20 mm and 50 mm.

Cutter ring and crushing edge specifications and dimensions within the above- specified ranges have proved to be advantageous for obtaining smaller pieces of sizes suitable for recycling with cutter ring sizes that are easily handled.

In an embodiment of the invention wherein the crushing edges are rounded with a radius of between 0.1 mm and 0.3 mm, preferably between 0.15 mm and 0.25 mm, most preferably between 0.18 mm and 0.22 mm.

It has been proved that the lifetime of the crushing edges is prolonged, if the edges are rounded with a radius within the above-specified ranges. In an embodiment of the invention, the surfaces of the crushing edges are coated with a layer of a reinforcing material, such as TiAlN-NANO (Titan-aluminium-nitrid- nano).

Such a coating has proven to be very advantageous for reducing the wear and improving the durability of the crushing edges, the coating material having a hardness of approximately 3600HV.

The letters HV indicates that the hardness of the material is given as a Vickers hardness number. Vickers hardness is a commonly used measure for the hardness of a material within the field of metallography. For the sake of comparison, it can be mentioned that the hardness of hardened steel typically will be in the range between 450HV and 950HV.

In an embodiment of the invention, the cutter ring consists of two or more thinner cutter ring modules with crushing edges being fixed together to form the cutter ring, each of the cutter ring modules having the same specifications and dimensions as the complete cutter ring with the exception of the width.

Constructing the cutter ring from a number of thinner cutter ring modules enables for obtaining cutter rings of different widths by simply using different numbers of identical cutter ring modules for each cutter ring.

In an aspect of the invention, it relates to a cutting machine as specified above, wherein the cutter rings are cutter rings like the ones also specified above.

In an aspect of the invention, it relates to a back pressure ring being designed so that when the back pressure ring is placed in one of two cutter assemblies arranged to rotate in opposite directions around parallel rotational axes, each of the cutter assemblies comprising a series of alternating cutter rings and back pressure rings fixed to each other to rotate with a common rotational speed, and the two cutter assemblies being arranged so that the cutter rings of the one cutter assembly interleave with the cutter rings of the other cutter assembly in a tight relation, the crushing edges of the cutter rings of one cutter assembly being in close contact with the back pressure rings of the other cutter assembly, and vice versa, a crushing effect parallel to the rotational axes is obtained between the crushing edges of the cutter rings of one cutter assembly and the back pressure rings of the other cutter assembly, wherein the back pressure ring is elastic.

In an embodiment of the invention, the elasticity is obtained by incorporating a layer of an elastic material, such as polyurethane, under a surface layer made from a more hard-wearing material, such as steel. The use of such a back pressure ring together with a cutter ring comprising a number of crushing edges extending in a substantially radial direction from the axis of rotation of the cutter ring, has shown to be very advantageous for obtaining an effective cutting of fibrous materials into smaller pieces of well-defined dimensions.

Making the back pressure rings elastic enables for creating a controlled crushing pressure between the back pressure ring and the crushing edges of the cutter rings of the opposing cutter assembly. Furthermore, the elasticity makes the tools self- compensating for wear and deflections.

In an embodiment of the invention, the back pressure ring is designed to exert a back pressure of between 20 N/mm ² and 400 N/mm ² , preferably between 80 N/mm ² and 250 N/mm ² at a deformation of 0.2 mm.

Back pressures within the specified ranges have proved to be advantageous for using the back pressure rings for cutting of different fibrous materials.

In an embodiment of the invention, the surface layer is coated with a layer of a reinforcing material, such as TiCN-22-NANO (Titan-carbo-nitrid-nano).

Such a coating has proven to be very advantageous for reducing the wear and improving the durability of the back pressure rings, the coating material having a hardness of approximately 3000HV.

In an embodiment of the invention, the back pressure ring consists of two or more thinner back pressure ring modules being fixed together to form the back pressure ring, each of the back pressure ring modules having the same specifications and dimensions as the complete back pressure ring with the exception of the width. Constructing the back pressure ring from a number of thinner back pressure ring modules enables for obtaining back pressure rings of different widths by simply using different numbers of identical back pressure ring modules for each back pressure ring.

In an aspect of the invention, it relates to a cutting machine as specified above, wherein the back pressure rings are back pressure rings like the ones also specified above. In an aspect of the invention, it relates to a method for disintegrating fibrous materials, such as glass fibre and felt carpets, said method comprising the step of: cutting the fibrous material into smaller pieces of controlled homogenous dimensions. Such a method is advantageous in that it enables for processing fibrous materials into a form suitable for being recycling instead of being deposited as is typical the case for this type of materials.

In an embodiment of the invention, the method further comprises the step of leading the smaller pieces of material collected from the working area through or passing by a heating device for melting away the threads used for stitching fibres of the fibrous material together, thus allowing the smaller pieces to disintegrating into single fibres.

Melting away the threads, which are typically made from polyester, has proved to be an advantageous way of facilitating the disintegration of the small pieces of some kinds of fibrous materials, especially glass fibre, into single fibres.

In an embodiment of the invention, the disintegration is performed by means of a cutting machine like the ones specified in the above-described embodiments of the present invention. In an aspect of the invention, it relates to a method for removing threads used for stitching fibres of fibrous material together, said method comprising the step of leading the fibrous material through or passing by a heating device for melting away the threads, thus allowing the material to disintegrate into single fibres.

Melting away the threads, which are typically made from polyester, has proved to be an advantageous way of facilitating the disintegration fibrous materials, especially glass fibre, into single fibres, because it involves no mechanical impact on the fibres, which could otherwise damage the fibres.

In an aspect of the invention, it relates to a method for renovating a cutter ring like the ones specified in the above-described embodiments of the present invention, said method comprising the steps of: removing a thin layer of material all over the rim and crushing edges of the cutter ring, for instance by means of a milling machine or a wire cutting machine, and re-coating the surfaces of the crushing edges with a layer of a reinforcing material, such as TiAlN-NANO (Titan-aluminium-nitrid-nano).

This method is advantageous in that it ensures that both the crushing edges and the cutting edges along the side of the cutter rings are sharpened during the renovation of the cutter ring.

The drawings

In the following, a few embodiments of the invention are described and explained in more detail with reference to the drawings, where fig. 1 illustrates a side view of a cutting machine according to an embodiment of the invention, fig.2 illustrates a perspective view of a cutting machine according to another embodiment of the invention, fig. 3 illustrates a side view of an electric motor and a gearing for a cutter assembly according to an embodiment of the invention, fig. 4a illustrates a perspective view of the cutter assemblies according to an embodiment of the invention, fig. 4b illustrates a close up view of a part of the cutter assemblies shown in fig.

4a, fig. 5a illustrates in a cross-sectional view the interaction between a crushing edge of a cutter ring of one cutter assembly with a back pressure ring of another cutter assembly according to an embodiment of the invention as seen from the side, fig. 5b illustrates the same interaction as seen from above, fig. 6a illustrates the interaction between a cutter ring of one cutter assembly and a cutter ring of another assembly according to an embodiment of the invention as seen from above, fig. 6b illustrates the same interaction as seen from the side, and fig. 6c illustrates an enlargement of a part of fig. 6b.

Detailed description

Figs. 1 and 2 illustrate a side view and a perspective view, respectively, of cutting machines 1 for cutting glass fibre fabric 16 according to embodiments of the invention. Apart from the furnace part 7-11 and the type of container 14, 15 in which the reusable fibres are accumulated, the two embodiments of the cutting machines 1 are substantially identical.

In the shown embodiments, the feeding device 2 basically consists of a conveyor belt 2, the conveying speed of which is adjusted to equal the peripheral velocity of the cutter rings 17, i.e. the tangential velocity of the crushing edges 18. In this way, it is assured that there will be no pulling or crowding of the fibre material 16 to be cut as it enters the cutting part of the machine 1 between the two cutter assemblies 3. The cutter machines according to the shown embodiments each comprise two cutter assemblies 3, the structure and function of which will be described in more detail below, is driven by an electric motor 4 to which it is mechanically connected through a gearing 5. In the shown embodiments, there is a motor 4 and a gearing 5 for each of the cutter assemblies 3, whereas in other embodiments of the invention, a common motor 4 and in some cases also a common gearing 5 may be used to drive the two cutter assemblies 3. Independent of the choice of configuration of motor(s) 4 and gearing(s), it is assured that the two cutter assemblies 3 are arranged to rotate in opposite rotational directions with a common rotational speed. After having been cut into square or rectangular pieces by the interaction of the two cutter assemblies 3 as described in more detail below, the fibre material 16 is conveyed through a furnace 8 by means of a heat-resistant conveyor belt 6. The purpose of this furnace 8 is to melt away the polyester threads used for stitching fibres of the fibrous material 16 together, thus allowing the pieces of fibre material 16 to disintegrate into single fibres.

Whereas fig. 2 is not very specific about the type and function of the furnace 8 used, fig. 1 illustrates in more detail how the furnace 8 takes in air through two air intakes 9, heats the air to about 450° C and causes the heated air to pass by the fibre material 16 by means of fans 10 inside the furnace 8. This means that the fibre material 16, which is transported through the furnace 8 between the conveyor belt 6 and an overlaying conveyor belt 7, is heated to about 450° C for about 5 seconds, causing the polyester threading to evaporate. Thus the stitching keeping the fibre material 16 in its fabric form is removed and the individual fibres of the material 16 are no longer bound together. The polyester vapour is sucked up through a chimney 11 that raises the temperature further to 850° C. At this temperature, the polyester steam is burned thus leaving no hazardous emissions from the furnace 8. Since the polyester only represents less than one percent or the glass fibre fabric 16, the C0 ₂ emissions are negligible. By this step of the process, the fibre material 16 has been disintegrated into even- sized fibres ready for reuse. After leaving the furnace 8 on the conveyor belt 6, the fibres are collected in a collector 23, from where the fibres are transported to a cyclone 13 by means of a screw conveyor 12. This screw conveyor 12 reduces the speed of the fibres, which would otherwise have been obtained due to the suction of the cyclone 13, and separates the dust from the reusable fibres.

Leaving the cyclone 13, the fibres are either packed directly in big bags 14, capable of accommodating up to 2 tons or more of fibres, and vacuum sealed for optimum space efficiency, which secures ease of transport and handling during transport, or they are accumulated in other types of containers 15 for further handling and packaging.

Fig. 3 illustrates a side view of an electric motor 4 and a gearing 5 for a cutter assembly 1 according to an embodiment of the invention, in which the gearing 5 is placed co-axially with the horizontally arranged cutter assembly 3 to be driven by the gearing 5, the corresponding electric motor 4 interacting with the gearing 5 being arranged to rotate around a vertical axis. In other embodiments of the invention, the arrangement of the gearing(s) 5 and the motor(s) 4 may be otherwise. Fig. 4a illustrates a perspective view of the cutter assemblies 3 according to an embodiment of the invention, and fig. 4b illustrates a close up view of a part of the cutter assemblies 3 shown in fig. 4a. Two cutter assemblies 3 are arranged to rotate in opposite directions around parallel rotational axes, and each of the cutter assemblies 3 comprises a series of alternating cutter rings 17 and back pressure rings 19 fixed to each other to rotate with a common rotational speed. Each of the cutter rings 17 comprises a number of crushing edges 18 extending radially from the axis of rotation, and the two cutter assemblies 3 are arranged so that the cutter rings 17 of the one cutter assembly 3 interleave with the cutter rings 17 of the other cutter assembly 3. As will be described more in detail below, the interaction of the two cutter assemblies 3 causes the fibre material 16 passing there between to be cut into relatively small square or rectangular pieces, the width y of which is decided by the width of the cutter rings 17, and the length x of which is decided by the tangential distance between the crushing edges 18 of the individual cutter rings 17.

Apart from producing the smaller pieces of fibre material 16, the cutting process also produces a substantial amount of dust. Therefore, the cutting section of the machine 1 has been provided with a suction device 24 in order to collect the smaller pieces of material 16 as well as dust and other unwanted by-products of the cutting process.

Fig. 5a and 5b illustrate how, according to an embodiment of the invention, a cutter ring 17 of one cutter assembly 3 interacts with a back pressure ring 19 of the other cutter assembly 3 to cut fibre material 16 passing there between along a line parallel to the rotational axes of the two cutter assemblies 3,

In fig. 5a, it is seen in a cross-sectional view how the right-most crushing edge 18 of the left-most cutter ring 17 is in close contact with the back pressure ring 19 of the other cutter assembly 3, thus creating a crushing effect there between. The crushing of the fibre material 16 taking place between the crushing edge 18 and the back pressure ring 19 divides the fibre material 16 into two pieces being separated by the crushing edge 18. Hence, for each crushing edge 18 brought into contact with the back pressure ring 19 during rotation of the two cutter assemblies 3, the fibre material 16 will be divided along the crushing edge 18, i.e. along a line parallel to the axes of rotation of the cutter assemblies 3. Therefore, the length of the smaller pieces of fibre material 16 being crushed by the crushing edges 18 of a given cutter ring 17 equals the tangential distance between two consecutive crushing edges 18 corresponding to the measure x as indicated in fig. 4b.

In order to overcome manufacturing tolerances of the cutting tools 17-19 and in order to avoid a deflection of the centre shafts (not shown) of the cutter assemblies 3, the back pressure rings 19 have been made slightly elastic, and the crushing pressure has been made adjustable by varying the distance between the cutter assemblies 3.

The back pressure rings 19 have been made elastic by incorporating a layer of elastic polyurethane 20 between the centre bring 25 and a surface layer 21 made from a hard-wearing coated material. Typically, the surface layer 21 will be about 5 mm thick and be made from tool steel hardened to a hardness of 58-64 HRC and coated with a layer of a reinforcing material, such as TiCN-22-NANO (Titan-carbo-nitrid- nano), in order to reduce the wear and improve the durability. This thickness has shown to be the optimum compromise between stiffness and flexibility of the surface layer 21.

The letters HRC indicates that the hardness of the material is given as a Rockwell hardness number. Rockwell hardness is a commonly used measure for the hardness of a material.

The choice of materials and dimensions for the back pressure ring 19 can be chosen specifically for any given application, depending on the back pressure desired to be exerted by the back pressure ring 19 at a given deformation, such as for instance 0.2 mm. The cutter rings 17 with the crushing edges 18 are typically made from tool steel hardened to a hardness of 58-64 HRC, and the crushing edges 18 are coated with a layer of a reinforcing material, such as TiAlN-NANO (Titan-aluminium-nitrid-nano), in order to reduce the wear and improve the durability. The use of such coatings for the back pressure rings 19 and the crushing edges 18 has shown to improve the projected lifetime of the cutter assemblies 3 substantially. Without the coating, the tools 17, 18, 19 of the cutter machine 1 would be worn down at a rate making it impossible to disintegrate the fibre material 16 in a cost-effective way. Moreover, it has been proved that the lifetime of the crushing edges 18 is further prolonged, if the edges 18 are rounded with a radius of approximately 0.2 mm.

The shape of the cutting knives 18 is extremely important in order to achieve a clean cut and an ideal feeding of the material 16 in between the cutter assemblies 3. A crushing edge 18 shape as illustrated in fig. 5a has proved to be especially advantageous for disintegration of fibrous materials 16. Each of the crushing edges 18 is formed by the ridge of a straight longitudinal structure, the cross-section of which is symmetric and basically triangular, and which extends all the way across the surface of the cutter ring 17 in a direction substantially parallel to the centre axis of the cutter ring 17. The distance between two consecutive crushing edges 18 is uniform all around the cutter ring 17 and larger than the width of each of the longitudinal structures so that a recess is formed between each pair of consecutive crushing edges 18.

The recess between two consecutive crushing edges 18 assures that the parts of the fibre material 16 not being crushed between a back pressure ring 19 and a crushing edge 18 will pass between the back pressure ring 19 and the cutter ring 17 without having any damage caused to the individual fibres thereof, thus maintaining the full strength of the fibres. Fig. 6a illustrates how two interleaving cutter rings 17 are arranged to rotate in a relation tight enough to assure a cutting effect perpendicular to the rotational axes of the cutter assemblies 3 between the edges 22 of the respective cutter rings 17 opposing each other.

This means that fibre material 16 passing between the two cutter assemblies 3 while overlapping two or more cutter rings 17 will be cut by the opposing edges 22 of two neighbouring cutter rings 17 like by a pair of scissors as seen more clearly in figs. 6b and 6c, which illustrate the same interaction as seen from the side.

Hence, on all positions along the cutter assemblies 3 where opposing edges 22 of two neighbouring cutter rings 17 interact with each other to produce such a cutting effect, the fibre material 16 will be divided along the edges 22, i.e. along a line perpendicular to the axes of rotation of the cutter assemblies 3. Therefore, the width of a given smaller piece of fibre material 16 being cut by the cutter rings 17 of the two cutter assemblies 3 equals the width of the cutter ring 17 between the edges 22 of which the smaller piece is located when being cut passing between the cutter assemblies 3, corresponding to the measure y as indicated in fig. 4b.

In the embodiment illustrated in figs. 6a-6c, the aperture in the centre of the cutter rings 17 (and also in the centre of the back pressure rings 19, which are not shown ) is hexagonal, allowing the cutter rings 17 and the back pressure rings 19 to be mounted on a hexagonal shaft (not shown) being rotationally locked to the shaft and, thus, to each other. In other embodiments, like the one shown in figs. 5a and 5b, the aperture may be circular or have other shapes, the rotational locking of the cutter rings 17 and the back pressure rings 19 being obtained by other means.

Also, as seen in fig. 6b, the size of the cutter rings 17 and the distance between the rotational axes of the two cutter assemblies 3 result in a "scissor" angle a between the two "scissor blades" formed by the edges 22 of the two neighbouring cutter rings 17. This "scissor angle" varies depending on the size of the cutter rings 17 and the back pressure rings 19 and, thus, the distance between their rotational axes. The optimum value of a depends on the type of fibre material 16 to be cut by the cutting machine 1 , and the dimensions of the cutter assemblies 3 are chosen accordingly.

List of reference numbers

1. Cutting machine

2. Feeding device

3. Cutter assembly

4. Motor for cutter assembly

5. Gearing for cutter assembly

6. Conveyor

7. Overlaying conveyor

8. Furnace

9. Air intake for furnace

10. Furnace fan

1 1. Furnace chimney

12. Screw conveyor

13. Cyclone

14. Big bag for packaging of reusable fibres

15. Container for accumulation of reusable fibres

16. Fibre material to be cut

17. Cutter ring

18. Crushing edge

19. Back pressure ring

20. Resilient layer of back pressure ring

21. Surface layer of back pressure ring

22. Cutting edge of cutter ring

23. Collector for fibres after heating

24. Suction device

25. Centre bring of back pressure ring x. Length of smaller piece of material cut by the cutting machine y. Width of smaller piece of material cut by the cutting machine a. "Scissor angle" between interacting edges of interleaving cutter rings